NIBCO UL Bronze Gate Valves - Manual (Page 6)

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6
when union nut joints are used. This gives lubrication to the joint so good tightening
pressures can be applied. The chain wrench or socket wrench should be used to tighten
the bonnet. Stop the union nut approximately at the same place where it was when the
valve was disassembled or possibly slightly past that mark. Remember any nick on the
surfaces on the bonnet sealing area assures leakage.
After the valve has been installed, the valve should be tested to make sure that it opens
and closes easily and that the bonnet joints or pipe joints are not leaking.
3.0 OPERATION
Gate valves should never be used for throttling purposes. They should be fully opened
or fully closed. If the valves were only slightly opened, wire drawing an erosion of the
wedge and seats would result. It is not recommended valves be tightly back-seated as
line contamination over a long period of time may lock up the valve causing problems
when the valve has to be closed.
4.0 TROUBLESHOOTING
4.1
LEAKAGE THROUGH THE STUFFING BOX
Leakage through the stuffing box packing may be stopped by tightening the packing nut. Do not
over tighten as excessive tightening may cause difficult operation of the valve and could cause
damage to the stem or packing nut.
If the gland has run out of travel, isolate and depressurize the valve for repacking or the addition
of more packing. Repacking of valves under pressure is not a recommended practice. This is
dangerous and could result in serious injury even if the valve appears to be back-seated.
Foreign matter may have accumulated on the back seat, or by accident the stem could be
knocked off the back seat position thereby allowing dangerous fluids to injure maintenance
personnel.
Remove the handwheel packing nut and gland to remove the old packing. After the packing is
removed, discard and do not try to put it back once it has been removed. Clean the stem and
examine it for damage. On very small valves the packing is sometimes rope and is sometimes
spiral wound around the stem and pushed into the stuffing box. Install the new packing which
may be one piece or split rings. If it is split ring rope packing install one ring at a time with the
diagonal cut in each ring being staggered 90° away from the cut in the ring below. Each ring
should be fully compressed in the stuffing box after it is placed in position before the next ring is
added.
Install the gland bushing and packing nut and tighten down. The packing nut should be
tightened only enough to prevent leakage. Pressurize the valve and check the packing for
leakage. Tighten as required.